The invention relates to a head harness for a respiratory mask that consists of a head plate and front, temple, and neck straps emerging from it that can be fastened to the respiratory mask with strap buckles in a six-point strap arrangement.
A similar head harness with a five-point strap arrangement in which one elastic strap in the forehead area, two elastic temple straps and two fixed straps across the neck emerge from a firm, inflexible head plate has been disclosed in EP 046 43 42, for example. The fixed neck straps are connected to the mask body by adjustable screws. Wearing a mask of this type is not sufficiently comfortable as the head harness of the respiratory mask may loosen and continuously needs readjustment to achieve safe fastening of the mask. This means that a firm fit of the mask is not guaranteed, especially under strain, as the mask easily slips under strain due to the elastic front strap. But if the straps are pulled too tight, they limit the head""s freedom of motion. The non-elastic head plate won""t slip when the mask is put on.
To hold the respiratory mask known from EP 0350 322 on the wearer""s head, it features a biaxially stretchable cap composed of multiple parts and domed to fit the shape of the head, while the head harness is mostly directly connected to the mask body. This head harness that encloses the head like a cap is sufficiently elastic to adapt to the shape of the head, however it does not ensure a firm fit when a respiratory filter is attached so that the mask can slip when in use, which reduces wearing comfort.
It is the problem of this invention to provide a head harness of the type mentioned at the outset for a respiratory mask that ensures a good fit of the straps for various head sizes while allowing free movement of the head and a firm fit as well as convenient and fast donning of the mask.
This problem is solved according to the invention by the head harness comprising the characteristics described in claim 1.
The subordinate claims disclose further characteristics and advantageous improvements of the invention.
Starting from the known head harness with a six-point strap fastening arrangement to the mask body wherein front, temple, and neck straps emerge from a head plate and connect to the mask, the general inventive idea here is that the head plate consists of a knitted fabric that is elastic in crosswise direction (X direction) only while it cannot be stretched in longitudinal direction (Y direction). The temple and neck straps that run in crosswise direction can also be stretched in this direction. The front strap that runs in longitudinal direction, however, is not elastic.
A head harness of this design is capable of compensating for differing head sizes, adjusting to different head shapes, and ensuring a firm fit and high wearing comfort. The forces that act in crosswise direction are evenly distributed across the elastic head plate while the longitudinal forces that act on the mask body are transmitted via the rigid front straps and absorbed by the head plate. As the forces are distributed elastically across the head plate, the mask fits firmly to its wearer""s face, and any longitudinal forces that occur are absorbed. Freedom of movement of the head is not reduced despite the tight-fitting respiratory mask.
In another aspect of the invention, the head and temple straps that emerge from the head plate can be fixedly preset to the respective head size and shape while only the neck straps are tightened after the wearer has put the mask on. In this way, the respiratory mask is correctly positioned and preset automatically after being put on. The neck straps are then tightened to the point at which the respiratory mask and head harness have a firm and comfortable fit on the head.
Another important characteristic of the invention is that each of the front, temple, and neck straps is a single, continuous strap. This distributes the forces in crosswise direction and the transmission of forces in longitudinal direction more evenly and increases the service life of the straps.
In an embodiment of the invention, the head plate is made of a heat and chemical-resistant knitted fabric known by the trade name NOMEX(copyright) that has the expansion characteristics described above and the shape of a double trapezoid along the upper rim of which the front strap runs, along the lower rim of which the neck strap runs, and along the joint elongated base line of the two trapezoids, i.e., along its widest section, the temple strap runs.